The present invention relates to methods and apparatus for displaying images, and more particularly, to methods and apparatus for increasing the perceived quality of displayed images.
Color display devices have become the principal display devices of choice for most computer users. The display of color on a monitor is normally achieved by operating the display device to emit light, e.g., a combination of red, green, and blue light, which results in one or more colors being perceived by a human viewer.
In cathode ray tube (CRT) display devices, the different colors of light are generated via the use of phosphor coatings which may be applied as dots in a sequence on the screen of the CRT. A different phosphor coating is normally used to generate each of the three colors, red, green, and blue resulting in repeating sequences of phosphor dots which, when excited by a beam of electrons will generate the colors red, green and blue.
As CRT""s age, the light output intensity tends to decrease for a given input intensity. Thus, older computer CRT display devices tend to be more difficult to read than new CRTs.
The term pixel is commonly used to refer to one spot in, e.g., a rectangular grid of thousands of such spots. The spots are individually used by a computer to form an image on the display device. For a color CRT, where a single triad of red, green and blue phosphor dots cannot be addressed, the smallest possible pixel size will depend on the focus, alignment and bandwidth of the electron guns used to excite the phosphors. The light emitted from one or more triads of red, green and blue phosphor dots, in various arrangements known for CRT displays, tend to blend together giving, at a distance, the appearance of a single colored light source.
In color displays, the intensity of the light emitted corresponding to the additive primary colors, red, green and blue, can be varied to get the appearance of almost any desired color pixel. Adding no color, i.e., emitting no light, produces a black pixel. Adding 100 percent of all three colors results in white.
Liquid crystal displays (LCDs), or other flat panel display devices are commonly used in portable computer devices in the place of CRTS. This is because flat panel displays tend to be small and lightweight in comparison to CRT displays. In addition, flat panel displays tend to consume less power than comparable sized CRT displays making them better suited for battery powered applications than CRT displays.
As the quality of flat panel color displays continues to increase and their cost decreases, flat panel displays are beginning to replace CRT displays in desktop applications. Accordingly, flat panel displays, and LCDs in particular, are becoming ever more common.
Color LCD displays are exemplary of display devices which utilize multiple distinctly addressable elements, referred to herein as pixel sub-elements or pixel sub-components, to represent each pixel of an image being displayed. In displays commonly used for computer applications, each pixel on a color LCD display usually comprises three non-square elements, i.e., red, green and blue (RGB) pixel sub-components. Thus, in such systems, a set of RGB pixel sub-components together make up a single pixel. LCD displays of this type comprise a series of RGB pixel sub-components which are commonly arranged to form stripes along the display. The RGB stripes normally run the entire length of the display in one direction. The resulting RGB stripes are sometimes referred to as xe2x80x9cRGB stripingxe2x80x9d. Common LCD monitors used for computer applications, which are wider than they are tall, tend to have RGB stripes running in the vertical direction. While RGB striping is common, R, G, B pixel sub-components of different rows may be staggered or off set so that they do not form stripes.
Other LCD pixel sub-component display patterns are also possible. For example, in some devices, each color pixel includes four square pixel sub-components.
While LCD devices offer some advantages over CRT display devices in terms of power consumption and weight, the perceived quality of LCD displays can be significantly impacted by viewing angle. The amount and color of light incident on an LCD device can also have a major impact on the perceived quality of images displayed on the LCD device. In addition, LCDs tend to have response characteristics which can vary widely from display to display and even among the same model displays made by the same manufacturer.
Perceived image quality of a display device depends not only on the physical characteristics of the display device, but also on the viewer""s ability to perceive such characteristics. For example, a viewer with a greater sensitivity to one color will perceive an image differently than a viewer with a greater sensitivity to another color. Viewers without the ability to perceive color at all are likely to perceive the quality of a color image somewhat differently than a viewer who can appreciate the supplied color information.
In view of the above, it is clear that physical display device characteristics, viewing conditions, e.g., ambient light, and a user""s ability to perceive various image characteristics all have an effect on the perceived quality of an image.
Given the quality of current display devices, it is apparent that for many applications improvements in image quality are not only desirable but also important to insure a user""s accurate interpretation of displayed images.
In view of the above, it is apparent that there is a need for new and improved methods and apparatus for displaying images such as text and graphics. It is desirable that at least some of the new methods and apparatus be capable of being used with both CRT as well as LCD display devices. Furthermore, in order to enhance the quality of images for specific viewers it is desirable that at least some display methods take into consideration how specific users perceive the images being displayed to them.
The present invention relates to methods and apparatus for increasing the perceived quality of displayed images. This is achieved in a variety of ways including the use of a plurality of device specific display characteristics and/or user preference or perception information when preparing images for display. The display device information (DDI) may be stored in what is referred to as a display device profile (DDP). User preference and/or perception information is stored in a user profile.
In accordance with one feature of the present invention display device output characteristics and/or ambient light conditions are monitored, e.g., on a periodic basis. The information obtained from the monitoring operation is used to update the DDP for the monitored display device. The information in the DDP is then used when generating an image for display.
Using information relating to a specific user""s viewing preferences and/or ability to perceive image characteristics such as color also improves the perceived quality of displayed images. By customizing display output to an individual user""s own physical perception capabilities and/or viewing characteristics it is possible to enhance the image quality perceived by the individual viewer as compared to embodiments which do not take into consideration individual user characteristics.
Display device information used in accordance with the present invention may be stored in a display device profile. This profile may be provided by the device manufacturer and loaded onto a computer system or other device at the time the system is configured for use with the display. Alternatively, the information may be stored in the display device and supplied to a system coupled thereto in response to a request for display device information. Yet another alternative is to maintain a database of display device information including information on a plurality of different display devices. The database may be maintained as part of the operating system. Device specific information is retrieved therefrom when a particular display device is used or installed.
The display device profile may include such information as the device""s date of manufacture and the type of display. It may also include information on the display device""s gamut, white point, gamma, pixel pattern, resolution, element shape and/or method of light modulation. The display device type may be CRT, reflective LCD, transmissive LCD, etc. The white point may be expressed in tristimulus values or R, G, B luminance values. Pixel pattern may be expressed in terms of the order or sequence of color pixel sub-components, e.g., RGB, BGR, RGGB, or any other implemented configuration. Display element shape information identifies, e.g., the shape of display pixels, e.g., square, rectangular, triangular or circular, and/or the shape of pixel sub-components which may also be square, rectangular, triangular or circular. The light modulation information indicates, e.g., whether color information is spatially or time modulated. In the case of spatial light modulation different color light is displayed at different positions on the screen. In the case of time modulation, different colors of light are displayed on the same portion of the screen at different times.
As discussed above, display device, e.g., profile information, may be periodically updated. This may be done by taking actual measurements of display device characteristics including light output. It may also be done by mathematically compensating for the age of the device and anticipated degradation in the device over time. In accordance with one feature of the invention, a display device""s gamut, gamma and white point values are updated in the display device profile to reflect measured or estimated changes due to age or use. Display age information may be obtained by subtracting display device installation information maintained by the operating system from current date information also maintained by the operating system. Alternatively, it can be obtained using date of manufacture information included in the original display device profile.
Ambient light conditions are measured, in accordance with one feature of the present invention, using the same device used to periodically measure display device light output characteristics. The ambient light condition information may include, e.g., information on whether a room light is on or off and/or information on the color components of the ambient light present. Ambient light condition information is used in an exemplary embodiment when controlling the display""s light output. For example, information that the ambient light includes relatively more blue than red or green light, e.g., due to the use of fluorescent lights, results in a controlled decrease in the relative intensity of blue light emitted by the display device.
With regard to user perception and/or preference information, this information may include information on a specific user""s ability to perceive color. Human color sensitivity can be measured by presenting the specific user with a simple test, e.g., displaying colors and then querying the user about his or her ability to perceive the displayed colors. The user perception information may also include user provided information on the user""s viewing angle and/or position relative to the display screen. Information about a user""s ability to perceive color and/or other perception information is stored in a user profile. The user profile can be maintained as part of the system""s operating system.
The above discussed methods of improving the perceived quality of displayed images can be used individually or in combination.
While the methods and apparatus of the present invention can be used to enhance the perceived image quality of most display devices, they are well suited for use with color flat panel display devices, e.g., LCD displays. In order to enhance the image quality of color LCD display devices, e.g., when rendering text, the luminous intensity of pixel sub-components can be independently controlled so that each pixel sub-component can be used to represent different portions of an image. While this technique of pixel sub-component control can provide a gain in effective resolution in one dimension, it can lead to color distortions which can be caused by the independent luminous intensity control of pixel sub-components. In such systems, color correction processing may be used to detect and reduce or eliminate what would be interpreted by most people as objectionable color distortions. Unfortunately, such color correction or compensation operations tend to reduce the benefit in terms of increased effective resolution that is provided by treating the different color pixel sub-components as independent luminance sources.
In accordance with one feature of the present invention, color correction processing is implemented as a function of at least some of the above discussed display device information, ambient light condition information and/or user perception information. For example, color correction processing may be performed as a function of a display device""s specific gamma values, detected ambient light conditions which will affect a human""s ability to perceive color and/or the user""s specific perception characteristics. For example, in the case of a color blind user, color compensation may automatically be disabled. In such a case, in LCD displays, an optimum or near optimum enhancement of image resolution may be achieved by treating pixel sub-components as independent luminance sources as opposed to a single luminance source. With color compensation disabled normally objectionable color distortions may exist in the displayed images. However, in the case of a color blind individual such distortions are not noticeable or objectionable and the increased effective resolution achieved by ignoring such color distortions is desirable.
Additional features, embodiments and benefits of the methods and apparatus of the present invention are discussed in the detailed description which follows.